The present invention relates generally to downhole milling operations, and more particularly to systems and methods of managing cuttings and debris resulting from milling a lateral borehole.
Hydrocarbons can be produced through relatively complex wellbores traversing a subterranean formation. Some wellbores can include multilateral wellbores and/or sidetrack wellbores. Multilateral wellbores include one or more lateral wellbores extending from a parent (or main) wellbore. A sidetrack wellbore is a wellbore that is diverted from a first general direction to a second general direction. A sidetrack wellbore can include a main wellbore in a first general direction and a secondary wellbore diverted from the main wellbore in a second general direction. A multilateral wellbore can include one or more windows or casing exits to allow corresponding lateral wellbores to be formed. A sidetrack wellbore can also include a window or casing exit to allow the wellbore to be diverted to the second general direction.
The casing exit for either multilateral or sidetrack wellbores can be formed by positioning a casing joint and a whipstock in a casing string at a desired location in the main wellbore. The whipstock is used to deflect one or more mills laterally (or in an alternative orientation) relative to the casing string. The deflected mill(s) penetrates part of the casing joint to form the casing exit in the casing string. Drill bits can be subsequently inserted through the casing exit in order to cut the lateral or secondary wellbore.
While milling the casing exit, cuttings and debris accumulate within the wellbore as a result of penetrating the metal casing. These cuttings and debris are typically removed to the well surface by circulation of a drilling fluid. As casing exits are increasingly being made at deeper well depths, flushing cuttings and debris to the surface becomes increasingly more difficult. This can also pose a significant problem with lateral exits that are made where the well casing may be near a horizontal exit. Inefficient or inadequate removal of cuttings and debris from the borehole could potentially result in increased difficulty in retrieving the milling system to the well surface.